Watlow Optimizing Your Process System with the Series 988 Controller - Manual (Page 22)

Optimizing Your Process System with the WATLOW Series 988
General Software Features
3.2
Overview:
The auto-tune feature allows the controller to
manipulate the process and calculate PID
values based on the process response. This
relieves the operator from the tedious task of
manually tuning the PID parameters to match
the characteristics of the thermal system.
The point at which the auto-tune takes place is
determined by the auto-tune set point
parameter. It is adjustable from 50 percent to
150 percent of the current set point, with 90
percent being the factory default setting. If the
auto-tune set point is 90 and the current
setpoint is 300 degrees, the control goes into
ON/OFF mode of control at 270 degrees (300
deg. x 0.9). The displayed setpoint is un-
changed and the bottom display information
alternates with tune
at a one-second rate
until the auto-tune is completed. Any changes
to the set point during an auto-tune will cause
the auto-tune sequence to start over, based on
the new set point.
Auto-tune
During an auto-tune the controller monitors
how fast the process increases and decreases,
and from this information calculates propor-
tional band, reset and rate values and auto-
matically enters them into non-volatile
memory.
To abort an auto-tune, set the auto-tune
prompt
to or press the AUTO/MAN
key twice, or cycle the power OFF and ON. The
previous PID parameters will be restored.
Requirements
The Series 988 can be ordered with two com-
plete sets of heat/cool PID sets. This requires
the enhanced software option. A single set of
PID parameters is available with the standard
software option.
TL
TL
W WA
PROCESS
L1 L2 L3 L4
DEV
% OUT DISPLAY
MODE
AUTO
MAN
SERIES 988
Oven
heater
temperature
sensor limit
sensor
limit
output 1 input 1
time →
auto-tune
complete
315 °
350 °
temperature
→
Sample Application:
In this example the oven needs to hold at 350 degrees F. To complete the
tuning sequence set the set point for 350 degrees and auto-tune by setting
the auto-tune prompt to
.